In recent years, with improvements in radio system transmission capabilities, the amounts of information exchanged between RFIC and BBIC (hereinafter, abbreviated as RF-BB) also increase. Moreover, it is also required, for still smaller mobile telephone devices, to reduce the number of RF-BB connection terminals and, for power savings, to make transmission speed variable in accordance with a communication system in operation.
To meet these requirements, the MIPI (Mobile Industry Processor Interface) alliance adopts high-speed serial interfaces of variable transmission speed type as a RF-BB interface system and is developing specifications thereof. More specifically, according to DigRFv4 interface, BBIC serves as a master while RFIC serves as a slave in terms of control, and the DigRFv4 interface is provided with a serial interface for transmission of control commands and transmission data mainly from BBIC and a serial interface, activated as necessary by a control command from BBIC, for transmission of state notifications and reception data mainly from RFIC. In the specifications of DigRFv4, transmission speed, the number of data paths, and the like are changed by transmitting a command through the serial interface.
Note that, for general serial interfaces, known is a method of transferring data from a master device to a slave device, as disclosed in PTL1, for example. That is, upon start of serial transfer, a master transmits a write command to a slave and, waiting until the arrival of an acknowledgement from the slave, transmits data.
{PTL 1} Japanese Patent Application Unexamined Publication No. 2005-228222